Functions and properties of CANopen devices (field devices), for example, are largely described using objects and are managed in an object dictionary. The object dictionary is represented in an electronic form in so-called EDS files (Electronic Data Sheet). EDS files are an inherent part of standardization in the CANopen environment (CiA DS306 and CiA DS311) and have a fundamental importance when the configuration in CANopen networks is involved. The file format specified by CiA ensures that the device descriptions of tools (for example ProCANopen) of different software companies can be read and processed. An EDS file (electronic data sheet) is therefore an example for a device description file which is permanently stored as firmware on a field device and contains all information concerning the device-specific parameters and operating modes of the device. Using the device description file, the device is properly configured or put into operation.
It is basically possible to make a distinction between field devices having a permanent configuration and field devices having an adjustable configuration. In a field device having a permanent configuration, it is clearly defined which process data (for example digital inputs or current speeds) are transmitted at what time and by which fieldbus (for example CAN) message. These settings cannot be modified later. Devices having a permanent configuration are often less expensive to purchase than devices of identical design which permit a configuration of the device during operation. The reasons therefore are the considerably simpler software structures and the transparent device implementation resulting therefrom. Field devices having an adjustable configuration have to be configured before being put into operation. All device parameters are defined using an appropriate configuration tool (ProCANopen, for example). The configuration thus obtained is then stored in the device. In a field device having an adjustable configuration, the network configuration created using the configuration tool is also stored in the field device provided that the devices support the “nonvolatile” storage (configuration data are not lost at a restart) of the configuration data. Alternatively, the device configuration can be stored in a configuration manager which performs the configuration of the configurable devices at a system startup. The configuration manager has to be defined already within the context of the network configuration. This approach permits the simple replacement of a defective device with a new device of identical design (simple maintenance of the system).
A gateway is furthermore adapted to couple two fieldbus systems with each other. The two fieldbus systems may in principle be such of an identical standard or different standards. According to the prior art, parameters or variables from the one fieldbus system (CANopen, for example) are made accessible to the second fieldbus system via a defined memory area in the coupling gateway. This however requires on the side of the second fieldbus system a complex association of storage locations or storage areas with the parameters or variables of the first system. Furthermore, filed devices in subsystems are not accessible without exact knowledge of the subsystem or of the field devices, and any modification of the subsystem requires an adaptation of the firmware. This in particular makes the access to parameters of the subsystems which are retrieved only occasionally in particular situations, for example for a diagnostic, more difficult.